So one of our amazing community members, Austin Taylor, just put together quite an exhaustive list of awesome software. Austin authors in math (and is currently in grad school getting his master's in the subject), but many of these software recommendations span across the disciplines. So thank you, Austin, for being so incredibly cool and putting this together. Let's give him a round of applause, folks. Enjoy!
Repositories/Libraries
Search for mathematical/statistical software and computer programming language source code (C, C++, Fortran) for ...

Many authors have come across the dilemma of not having a TI calculator to use when a question, or a group of questions, asks for one. Before you go out of your way to purchase a new TI calculator, try the TI Emulator! The TI Emulator works just like a graphing calculator, and actually makes it easier to transfer your graphs from the calculator to your solution/s. All you need to do is save the image as a .jpg ...